Detailed Prepress Operation - Separation Operation (1)

Second application of color separation

The main task of applying color separation is to analyze the configuration of technical points and technical control parameters in image composition and color separation processing of common manuscripts in electronic color separation platemaking, and to analyze the internal laws. To improve the image copy quality and job efficiency of the application color separation job.

First, the color contrast operation of the original contrast is too small

Too small contrast of the original refers to the size of the image's density. There are two important reasons for the production of this kind of image. One is that the original creators used a series of techniques to produce special artistic effects (such as high-profile images), and the other is that the original creators were not skilled in the technique. Or control mistakes (such as underexposure). The following four types are common in electronic color separations. (1) High-profile originals, (2) low-key originals, (3) overexposed originals, and (4) under-exposed originals. Among them, the high-profile and low-key manuscripts of (1) and (2) are consciously shot and produced by the manuscript author. The separation of color should be based on the characteristics of faithful manuscripts. Excessively overexposed and underexposed manuscripts of (3) and (4) are caused by improper handling during photography or photographic processing, and appropriate compensation is required for color separation.

The high-profile manuscript is shown in a of Figure 6.1, which is only in the high light to midtone range. If the black field is set at the deepest part of the original during the color separation scan, the entire tone of the scanned image will be hardened, and the copied image will lose the high-profile characteristics of the original document and become like a normal photograph. Therefore, high-precision manuscript separation should adopt the white/black calibration of the curve (1) in Figure 6.2, otherwise the color separation result will be the same as the curve (2). Therefore, during the color separation operation, the artistic features of high-profile manuscripts should be fully understood when setting up the black court. Select a high density level on the gray scale to use as the black field of the image or select the darkest part of the original to reduce the black scale calibration values ​​C, M, Y, and BK, and increase the intermediate tone level appropriately. , can fully reproduce the characteristics of high-profile manuscripts. Therefore, the black field calibration is the key to its color separation technology. Selecting a dark field as much as possible when selecting a black field on a ladder scale can make the copying effect better.

A low-key manuscript is the opposite of a high-profile manuscript. As shown in b of Figure 6.3, the image has only intermediate and dark tone levels, but is different from the under-exposed manuscript. Therefore, when performing color separation, a low-density area should be selected as a white field on the ladder scale, and the black field selection should also be higher than the density value in the darkest part of the original document. No changes to the hierarchy are required for correction.

The image of an overexposed original is similar to a high-profile original but it is due to overexposure in photography. Therefore, when the color separation, the white field should be selected in the original density of the normal position, the black field is selected in the original density of the most people. When the gradation is corrected, the midtones are properly increased, as shown in curve (2) in Figure 6.2. In contrast, under-exposed manuscripts are similar to low-profile manuscripts and are caused by underexposure in photography. When the color separation is calibrated, white-field is set at the position where the manuscript is high-profiled. The black field is set at the position where the density is the darkest and the middle tone is appropriate. reduce.

(to be continued)